JP2021123719A - Coating composition, coated metal plate, drawn and ironed can, and method for manufacturing the same - Google Patents

Abstract

To provide a coating composition which enables making of a coated metal plate and a drawn and ironed can having high adhesion to a base material without peeling of a coating during canning in can processing such as drawing and ironing molding.SOLUTION: A coating composition for a drawn and ironed can contains: a polyester resin having a glass transition temperature Tg of equal to or higher than 60°C as a main agent resin; and a resol type phenol resin and/or amino resin as a curing agent; and an organic sulfonic acid-based and/or organic phosphorus acid-based acid catalyst as a curing catalyst, in which the content of a curing catalyst is less than 0.3 pts.mass with respect to 100 pts.mass of the main agent resin.SELECTED DRAWING: Figure 1

Description

The present invention relates to a coating composition and a coated metal plate coated with the coating composition. Furthermore, the present invention relates to a squeezing can using the coated metal plate and a method for manufacturing the same.

Squeezing and ironing is known as a processing method for producing seamless cans widely used for beverage cans and the like. This drawing is a cylinder consisting of a body without side seams and a bottom that is seamlessly connected to the body by punching a metal plate such as an aluminum plate or steel plate into a circle and drawing. It is a processing method in which a container body is thinned by molding it into a shaped cup and then ironing it, and the seamless can obtained by this method is called a squeezing iron can.

As a method for producing this squeezed iron can, for example, a method using a laminated metal plate previously coated with a thermoplastic resin film such as polyethylene terephthalate as a metal plate is known. According to this method, since the thermoplastic resin film has a lubricating function when drawing and ironing, it is possible to perform drawing and ironing under dry conditions without using a liquid coolant (water-based lubricant). Compared to the case of squeezing and ironing using the liquid coolant of the above, there is an advantage that it contributes to the reduction of the environmental load. On the other hand, the thermoplastic resin film in the laminated metal plate used in this method has a certain thickness or more for the convenience of film formation, which may cause a problem in terms of economy.

In contrast to the above method, a method of producing a squeezed iron can by squeezing and ironing a coated metal plate has been proposed (Patent Document 1). According to this method, when a metal plate on which a coating film (coating film) is formed is squeezed and ironed, the coating film has a lubricating function, so that the squeezing and ironing can be realized under dry conditions. .. Further, by making the coating film a thin film, it is economically excellent.

Japanese Patent No. 3872998 Japanese Patent No. 4091266

However, in the above-mentioned method for manufacturing a can of squeezing and ironing using a coated metal plate, sufficient performance is obtained from the viewpoints of can manufacturing processability of the coating film, substrate adhesion, flavor adhesion resistance of the contents, and the like. Nothing that meets the requirements has yet been proposed.

That is, in the drawing and ironing process, it is required that the coating film defect does not occur during the can manufacturing process (can manufacturing processability) and that the coating film does not peel off from the base material (base material adhesion).
In addition, when the contents are filled in the container manufactured by the above-mentioned squeezing and ironing process, if the flavor components (fragrance components) such as limonene contained in the contents are contained in the coating film, the contents Since the flavor of the can changes, it is required that the coating film on the inner surface side of the can does not adhere (flavor adhesion resistance).

The present inventors have diligently studied to solve the above problems. As a result, in the coating composition containing the polyester resin, the curing agent and the curing catalyst, the polyester resin having a glass transition temperature of a predetermined temperature or higher is used, and the curing catalyst is blended to promote the cross-linking reaction between the polyester resin and the curing agent. The present invention has been conceived by finding that the above problems can be compatible with each other at a high level by setting the amount of the resin to less than a predetermined amount.

In order to achieve the above object, the coating composition in one embodiment of the present invention comprises (1) a polyester resin having a glass transition temperature of 60 ° C. or higher as a main agent resin, and a resol type phenol resin and / or an amino resin as a curing agent. The curing catalyst contains an organic sulfonic acid-based acid catalyst and / or a phosphoric acid-based acid catalyst, and the content of the curing catalyst with respect to 100 parts by mass of the main resin is less than 0.3 parts by mass.
In the above (1), (2) the content of the curing catalyst with respect to 100 parts by mass of the base resin is preferably 0.1 part by mass or less.
In the above (1) or (2), it is preferable that the acid value of (3) the base resin is less than 20 mgKOH / g.
In the above (1) to (3), (4) the content of the curing agent with respect to 100 parts by mass of the main agent resin is preferably 4 to 30 parts by mass.
Further, in the coated metal plate for a squeezing iron of the present embodiment, (5) a coating film of the coating composition according to any one of (1) to (4) above is formed on the metal surface of at least one side of the metal plate. It is made up of.
In (5) above, (6) the 180 ° peel strength of the coating film is preferably 1N / 15 mm or more.
The squeezed iron can of the present embodiment is made of (7) a coated metal plate for a squeezed iron can according to (5) or (6) above.
In the above (7), the thickness of the coating film at the center of the side wall of the can body on the inner surface and / or the outer surface of (8) is 20 to 75% of the thickness of the coating film on the bottom of the can. ..
The method for manufacturing a squeezed iron can of the present embodiment is as follows: (9) The coated metal plate for a squeezed iron can according to (5) or (6) above is squeezed and squeezed at a squeezing rate of 25 to 80%. It is characterized by doing.
The squeezed iron can of the present embodiment is (10) a squeezed iron can having a coating film on the inner surface and / or the outer surface, wherein the coating film is a main resin, a polyester resin having a glass transition temperature of 60 ° C. or higher, and a curing agent. It contains a resole-type phenol resin and / or an amino resin as a curing catalyst, and an organic sulfonic acid-based acid catalyst and / or a phosphoric acid-based acid catalyst as a curing catalyst, and the content of the curing catalyst with respect to 100 parts by mass of the base resin is 0.3 mass by mass. It is also characterized in that the thickness of the coating film at the center of the side wall of the can body is 20 to 75% of the thickness of the coating film at the bottom of the can.
In the above (10), it is preferable that the content of the curing catalyst with respect to 100 parts by mass of the main agent resin (11) is 0.1 parts by mass or less.
In the above (10) or (11), it is preferable that the metal plate (12) is formed from a coated metal plate having a coating film on at least one side.

According to the coating composition of the present invention, in the can-making process such as squeezing and ironing, it is provided to provide a coated metal plate for squeezing and squeezing cans having high substrate adhesion without peeling of the coating film during can-making. Is possible.

It is explanatory drawing for 180 degree peel strength measurement. It is explanatory drawing for 180 degree peel strength measurement. It is explanatory drawing for 180 degree peel strength measurement.

<Paint composition>
Hereinafter, the coating composition of the present invention will be described using embodiments, but the present invention is not limited to the following embodiments.
The coating composition of the present embodiment is characterized by containing a main agent resin, a curing agent, and a curing catalyst. Specifically, a polyester resin having a glass transition temperature (Tg) of 60 ° C. or higher is used as a main resin, a resole-type phenol resin and / or an amino resin as a curing agent, and an organic sulfonic acid-based and / or a phosphoric acid-based curing catalyst. It contains an acid catalyst.

In the present embodiment, the main resin is a polyester resin having a glass transition temperature of 60 ° C. or higher. The reason is as follows.
When the contents are filled in a can container manufactured by the above-mentioned squeezing and ironing process, if the flavor component (fragrance component) such as limonene contained in the contents is absorbed in the coating film, the flavor of the contents is lost. Since it changes, it is required that the coating film on the inner surface side of the can does not adhere (flavor adhesion resistance).
When the glass transition temperature of the polyester resin is less than 60 ° C., the motility of the resin becomes high, so that the flavor component easily diffuses into the coating film, the flavor component adheres to the coating film increases, and the flavor resistance resistance increases. In addition to the possibility of reducing the adhesion, the corrosion resistance and the retort resistance may be reduced, which is not preferable.
The glass transition temperature of the polyester resin is in the range of 60 ° C. or higher, preferably 60 to 120 ° C., more preferably higher than 65 ° C. and 120 ° C. or lower, further preferably 67 to 100 ° C., and particularly preferably 70 to 90 ° C. Is desirable.

In the present embodiment, the polyester resin as the main resin may be a blend of a plurality of polyester resins having different glass transition temperatures. _{In that case, the Tg mix of the} polyester resin blend calculated by the following formula (1) may be 60 ° C. or higher, preferably 60 to 120 ° C., more preferably higher than 65 ° C. and 120 ° C. or lower, still more preferably 67. It is desirable that the temperature is in the range of ~ 100 ° C., particularly preferably 70 to 90 ° C.
1 / Tg _mix = (W1 / Tg1) + (W2 / Tg2) + ... + (Wm / Tgm) ... (1)
W1 + W2 + ... + Wm = 1
In the formula, Tg _mix represents the glass transition temperature (K) of the polyester resin blend, and Tg1, Tg2, ..., Tgm is the glass transition of each polyester resin (polyester resin 1, polyester resin 2, ... polyester resin m) used. Represents temperature (K). Further, W1, W2, ..., Wm represent the weight fraction of each polyester resin (polyester resin 1, polyester resin 2, ... polyester resin m).

As a method for measuring the glass transition temperature, a known method can be applied, and for example, it can be performed at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC).

The acid value of the polyester resin, which is the main resin of the present embodiment, is preferably less than 20 mgKOH / g, preferably 15 mgKOH / g or less, and more preferably 0.5 to 11.5 mgKOH / g. When the acid value of the polyester resin is 20 mgKOH / g or more, the number of reaction points with the curing agent increases, so that the crosslink density of the coating film increases, and preferable can-making processability can be obtained during the production of squeezed iron cans. It is not preferable because it may not be possible.

When the main resin is a blend of two or more types of polyester resins, the sum of the values obtained by multiplying the acid value of each polyester resin by the mass fraction is the average acid value of the blend. (AV _mix ), and the average acid value thereof may be within the above-mentioned acid value range.

In the main agent resin of the present embodiment, examples of the polyvalent carboxylic acid component constituting the polyester resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and naphthalenedicarboxylic acid, succinic acid, glutaric acid, and adipic acid. Aliphatic dicarboxylic acids such as azelaic acid, sebacic acid, dodecandioic acid, dimer acid, unsaturated dicarboxylic acids such as (anhydrous) maleic acid, fumaric acid, terpene-maleic acid adduct, 1,4-cyclohexanedicarboxylic acid, tetrahydro Trivalent or higher polyvalents such as alicyclic dicarboxylic acids such as phthalic acid, hexahydroisophthalic acid and 1,2-cyclohexendicarboxylic acid, (anhydrous) trimellitic acid, (anhydrous) pyromellitic acid, and methylcyclohexentricarboxylic acid. Examples thereof include carboxylic acids, and one or more of these can be selected and used.

In the present embodiment, from the viewpoints of flavor sorption resistance, corrosion resistance, retort resistance, etc., aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid among the polyvalent carboxylic acid components constituting the polyester resin are used. The ratio is preferably 80 mol% or more, more preferably 80 to 100 mol%, and particularly preferably 90 to 100 mol%.
Further, a linear aliphatic dicarboxylic acid having a carbon number of more than 6 such as adipic acid, azelaic acid, sebacic acid, and dodecandioic acid is contained in the residual ratio of the aromatic dicarboxylic acid, that is, in an amount of 20 mol% or less. However, a linear aliphatic dicarboxylic acid having a carbon number of more than 6 has a high affinity with a hydrophobic flavor component such as limonene and tends to be easily sorbed. Therefore, when a coating film is formed using a polyester resin containing a large amount of linear aliphatic dicarboxylic acid having a carbon number of more than 6 as the polyvalent carboxylic acid component constituting the polyester resin, the flavor adhesion of the coating film is inferior. Will be. Therefore, the proportion of the linear aliphatic dicarboxylic acid having a carbon number of more than 6 in the polyvalent carboxylic acid component constituting the polyester resin is less than 20 mol%, preferably less than 10 mol%, and more preferably less than 7 mol%. , More preferably less than 5 mol%.

When the polyester resin is a blend of two or more types of polyester resins, it is a linear aliphatic compound having a carbon number of more than 6 in the total of all polyvalent carboxylic acid components constituting the polyester resin blend. It is desirable that the proportion of dicarboxylic acid is less than 20 mol%, preferably less than 10 mol%, more preferably less than 7 mol%, still more preferably less than 5 mol%.

On the other hand, the polyhydric alcohol component constituting the polyester resin is not particularly limited, and is ethylene glycol, propylene glycol (1,2-propanediol), 1,3-propanediol, 1,4-butanediol, 1, 2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentane Glycol, 2-ethyl-2-butyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 1-methyl-1,8-octanediol, 3-methyl-1,6-hexane Aliphatic glycols such as diols, 4-methyl-1,7-heptanediols, 4-methyl-1,8-octanediols, 4-propyl-1,8-octanediols, 1,9-nonanediols, diethylene glycols, Ether glycols such as triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, tricyclodecaneglycols, It can be used alone or in combination of two or more from alicyclic polyalcohols such as water-added bisphenols, trivalent or higher polyalcohols such as trimethylolpropane, trimethylolethane, and pentaerythritol.
In the present embodiment, among the above polyhydric alcohol components, ethylene glycol, propylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 2-methyl-1,3-propanediol, and diethylene glycol are polyesters. It can be suitably used as a component constituting the resin. In particular, from the viewpoint of flavor sorption resistance, ethylene glycol, propylene glycol, neopentyl glycol, 2-methyl-1,3-propanediol and 1,4-cyclohexanedimethanol among the polyhydric alcohol components constituting the polyester resin It is desirable that the ratio of at least one selected from the above is 70 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more.

The number average molecular weight (Mn) of the polyester resin is not limited to this, but is preferably 1,000 to 100,000, particularly preferably 3,000 to 50,000, and further, from the viewpoint of can-making processability. It is preferably in the range of 5,000 to 20,000. preferable. If it is smaller than the above range, the coating film becomes brittle and the can-making processability may be inferior, and if it is larger than the above range, the paint stability may be lowered.

Further, the polyester resin is preferably an amorphous polyester resin from the viewpoint of can manufacturing processability, dent resistance, and paint formation. Here, amorphous means that the melting point of the crystal component is not clearly shown in the measurement by the inspection scanning calorimeter. In the case of a non-crystalline polyester resin, a coating film having excellent solubility in a solvent, easy to make into a paint, and excellent can-making processability and dent resistance can be formed as compared with a crystalline polyester resin. ..

The hydroxyl value of the polyester resin is not limited to this, but is preferably 20 mgKOH / g or less, more preferably 10 mgKOH / g or less.

<Hardener>
Next, the curing agent used in the coating composition of the present embodiment will be described. As the curing agent used in the present embodiment, a resol type phenol resin and / or an amino resin can be preferably used from the viewpoint of hygiene and curability.

In the present embodiment, the resol-type phenol resin is obtained by reacting a phenol monomer and formaldehyde in the presence of an alkaline catalyst. For example, as phenol monomers, o-cresol, p-cresol, p-tert-butylphenol, p-ethylphenol, 2,3-xylenol, 2,5-xylenol, phenol, m-cresol, m-ethylphenol, 3,5 Examples thereof include -xylenol and m-methoxyphenol, which can be used alone or in admixture of two or more. Among them, m-cresol is preferable as the phenol monomer from the viewpoint of curability.
Further, one in which a part or all of the contained methylol groups are alkyl etherized with alcohols having 1 to 12 carbon atoms can also be used.
In the present embodiment, from the viewpoint of reactivity and compatibility with the main resin, a part or all of the contained methylol groups which are alkyl etherified with alcohols having 1 to 12 carbon atoms can be preferably used. It is possible, and in particular, a methylol group of a resol-type phenol resin derived from m-cresol (m-cresol-based resol-type phenol resin) is alkyl etherized with n-butanol is preferable.
The number average molecular weight (Mn) of the resole-type phenol resin is preferably in the range of 500 to 3,000, preferably 800 to 2,500.

In the present embodiment, the amino resin includes, for example, a reaction between an amino component such as melamine, urea, benzoguanamine, acetguanamine, steroguanamine, spiroganamin, dicyandiamide, and an aldehyde component such as formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde. Examples thereof include the methylolated amino resin obtained by. The amino resin also includes a methylolated amino resin in which the methylol group is alkyl etherized with an alcohol having 1 to 6 carbon atoms. These can be used alone or in combination of two or more. From the viewpoint of hygiene, a methylolated amino resin (melamine resin) using melamine and a methylolated amino resin (benzoguanamine resin) using benzoguanamine are preferable.

As the benzoguanamine resin, a benzoguanamine resin obtained by alkyl etherifying a part or all of the methylol groups of the benzoguanamine resin with an alcohol such as methanol, ethanol, n-butanol or i-butanol, particularly methyl etherified benzoguanamine etherified with a methyl alcohol. A resin, a butyl etherified benzoguanamine resin butyl etherified with butyl alcohol, or a mixed etherified benzoguanamine resin with methyl ether and butyl ether etherified with both methyl alcohol and butyl alcohol is preferable. As the butyl alcohol, isobutyl alcohol and n-butyl alcohol are preferable.

As the melamine resin, a melamine resin obtained by alkyl etherifying a part or all of the methylol groups of the melamine resin with an alcohol such as methanol, ethanol, n-butanol or i-butanol, particularly methyl etherified melamine etherified with a methyl alcohol. A resin, a butyl etherified melamine resin butyl etherified with butyl alcohol, or a mixed etherified melamine resin with methyl ether etherified with both methyl alcohol and butyl alcohol and butyl ether is preferable.

Of the above, the curing agent used in the coating composition of the present embodiment is particularly preferably a resol-type phenol resin from the viewpoint of can-making processability, heat resistance, and the like of the coating film.

In the present embodiment, the content of the curing agent is 3 parts by mass or more, preferably 3 to 50 parts by mass, more preferably 4 to 30 parts by mass, and further preferably 4 to 30 parts by mass with respect to 100 parts by mass of the polyester resin which is the main resin. It is 6 to 20 parts by mass. If the content of the curing agent is less than the above range, the curing property becomes insufficient, and when a squeezed iron can is formed, the heat resistance, retort resistance, content resistance, corrosion resistance, etc. of the coating film are insufficient. It is not preferable because it may be possible. If the content of the curing agent exceeds 50 parts by mass, curing may proceed excessively, resulting in deterioration of the can-making processability and impact resistance of the coating film.

<Curing catalyst>
The coating composition of the present embodiment contains a curing catalyst for accelerating the cross-linking reaction between the main resin and the curing agent. Examples of the curing catalyst include acid catalysts.
Specific examples thereof include organic sulfonic acid-based and / or phosphoric acid-based acid catalysts. Examples of the organic sulfonic acid-based acid catalyst include acid catalysts such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenedisulfonic acid, and amine neutralized products thereof. On the other hand, as the phosphoric acid-based acid catalyst, phosphoric acid, alkyl phosphoric acid, or an amine neutralized product thereof or the like can be used.
Of these, one type or two or more types can be used in combination. Among the above acid catalysts, dodecylbenzenesulfonic acid and this amine neutralized product are preferable.

In the coating composition of the present embodiment, the content of the curing catalyst is less than 0.3 parts by mass, preferably less than 0.2 parts by mass, as a solid content with respect to 100 parts by mass of the polyester resin which is the main resin. It is preferably 0.1 part by mass or less, more preferably 0.03 to 0.1 part by mass. In the present embodiment, when the curing catalyst is an amine neutralized product of the acid catalyst (for example, an amine neutralized product of dodecylbenzenesulfonic acid), the content of the acid catalyst excluding the amine is within the above range. If it is good.

The reason for this is as follows.
That is, in the coated metal plate, the adhesion between the surface of the base material (for example, aluminum) and the coating film is considered to be largely due to the acid-base interaction between the carboxyl group contained in the polyester resin and the base material. Therefore, in principle, it can be said that the more carboxyl groups in the polyester resin (that is, the higher the acid value of the polyester resin), the higher the adhesion to the base material. However, when the acid value of the polyester resin becomes higher than a predetermined value, the crosslink density of the coating film becomes high, which may result in insufficient can-making processability.
Therefore, in the present embodiment, even when a polyester resin having a low acid value, which tends to have a lower substrate adhesion than a polyester resin having a high acid value, is used, it is cured in order to impart sufficient substrate adhesion. The content of the catalyst is limited to the above range.

Conventionally, it has been considered that the curability of the resin is lowered when the content of the curing catalyst in the coating composition containing the polyester resin and the curing agent is reduced, but particular attention is paid to the blending amount of the curing catalyst. It wasn't done. That is, conventionally, it has not been known among those skilled in the art that the content of the curing catalyst affects factors other than curability.
In the present embodiment, it has been confirmed that when the content of the acid catalyst in the coating composition containing the polyester resin and the curing agent is reduced to a small amount, the adhesion of the coating film to the substrate is improved.
The reason for this is that the present inventors cause an acid-base interaction between the sulfonic acid group in the acid catalyst (for example, dodecylbenzenesulfonic acid) and the base material (for example, aluminum) to cause the coating film and the base material. It was speculated that the acid catalyst was locally present at the boundary of. As a result, it was presumed that the adhesion between the polyester resin and the base material in the coating film was lowered. Even when the curing catalyst is other than the organic sulfonic acid-based acid catalyst, the above estimation holds for an acid catalyst capable of causing an acid-base interaction with the substrate (for example, a phosphoric acid-based acid catalyst).

As a result of repeating experiments by the present inventors based on the above estimation, when the amount of the curing catalyst to be blended in the coating composition is changed, even if the content of the curing catalyst is made smaller than before, the curability is adversely affected. It was found that the results that can withstand practical use can be obtained in terms of substrate adhesion.
That is, even when the acid value of the polyester resin is low (for example, even if the acid value is 2.0 mgKOH / g or less), by setting the content of the curing catalyst to a predetermined value or less, the substrate adhesion can be obtained. It was found that the decrease can be suppressed, and the present invention was conceived.

<Paint composition>
The coating composition of the present embodiment contains at least the above-mentioned specific polyester resin as the main agent (main component), the resole-type phenol resin and / or the amino resin as the curing agent, the solvent, and the acid catalyst. In the coating composition of the present embodiment, the content (mass ratio) is the highest among the solid components (nonvolatile components excluding volatile substances such as water and solvent) forming the coating film in the coating composition. The component with a large amount of water is defined as the main agent (main component).
Examples of the type of the coating composition of the present embodiment include a solvent-based coating composition and a water-based coating composition, but in the present invention, the solvent-based coating composition is preferable from the viewpoint of coatability and the like.

<Solvent>
When the coating composition of the present embodiment is a solvent-based coating composition, it contains the above-mentioned polyester resin, curing agent, acid catalyst, and an organic solvent as a solvent. The solvent-based paint composition in the present embodiment is a paint in which a main resin, a curing agent, etc. are dissolved in a known organic solvent, and the mass ratio of the organic solvent in the paint composition. Is defined as a coating composition in which is 40% by mass or more.
Examples of the organic solvent include toluene, xylene, aromatic hydrocarbon compounds, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, ethylene glycol monoethyl ether acetate, and diethylene glycol monoethyl ether acetate. , Ethylene glycol monoacetate, methanol, ethanol, butanol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, solvent naphtha, etc., select one or more in consideration of solubility, evaporation rate, etc. Is used.

<Additives>
The coating composition of the present embodiment may further contain known additives as long as the object of the present invention is not impaired. For example, it may contain a lubricant, a pigment, a leveling agent, an antifoaming agent and the like. The lubricant that can be added to the coating composition of the present embodiment is not particularly limited, but is, for example, a fluorine-based wax such as a fatty acid ester wax, a silicon-based wax, or a polytetrafluoroethylene that is an esterified product of a polyol compound and a fatty acid. Examples thereof include polyolefin waxes such as waxes and polyethylenes, paraffin waxes, lanolin, montan waxes, microcrystallin waxes, carnauba waxes, silicon-based compounds, and vaseline. These lubricants can be used alone or in admixture of two or more.

<Painted metal plate>
Next, the painted metal plate of the present embodiment will be described. It is desirable that the coated metal plate of the present embodiment has a coating film on at least one surface of the metal plate, preferably on the inner surface of the can, and more preferably on both sides of the metal plate. The coating film can be formed by applying the above-mentioned coating composition on a metal plate and then baking it by heating or the like, and preferably the coating film is formed on the metal surface of the metal plate ( The coating film is formed so as to be in direct contact with the metal plate). The coated metal plate of the present embodiment is a metal plate suitable for a squeezing iron can.

Examples of the metal plate preferably used for the coated metal plate of the present embodiment include a hot-stretched steel sheet, a cold-rolled steel sheet, a hot-dip zinc-plated steel sheet, an electrozinc-plated steel sheet, an alloy-plated steel sheet, an aluminum-zinc alloy-plated steel sheet, and an aluminum plate. Examples thereof include aluminum alloy sheets, tin-plated steel sheets, stainless steel sheets, copper plates, copper-plated steel sheets, tin-free steels, nickel-plated steel sheets, ultrathin tin-plated steel sheets, and chrome-treated steel sheets. If necessary, those subjected to various surface treatments may be used.

Regarding the coated metal plate of the present embodiment, as a method for forming a coating film, the above-mentioned coating composition can be applied to the above-mentioned metal plate by a known coating method such as roll coater coating or spray coating. Further, after painting, a coating film can be obtained by baking with a heating means such as a coil oven.

The baking conditions of the coating composition are appropriately adjusted depending on the polyester resin, the curing agent, the type of the metal base material, the coating amount, etc., but the above-mentioned coating composition has a baking temperature in order to obtain sufficient curability. It is heat-cured at a temperature of 150 ° C. to 350 ° C., preferably higher than 200 ° C. and 320 ° C. or lower, under the conditions of 5 seconds or longer, preferably 5 seconds to 30 minutes, and particularly preferably 5 seconds to 180 seconds.

Although coating weight is not particularly limited, with the coating weight after drying and baking 300 mg / dm ² or less, preferably ^{20mg / dm 2 ~200mg / dm 2} , more preferably ^{30mg / dm 2 ~150mg / dm 2} , further preferably it is preferably in the range of ^{40mg / dm 2 ~140mg / dm 2} . The weight of the coating film is appropriately determined depending on the use of the coated metal plate. The baking conditions of the coating film are appropriately adjusted depending on the solvent used, the type and thickness of the metal material to be coated, the coating speed, and the like.

In the coated metal plate of the present embodiment, a coating film is formed on the metal plate as described above, but the 180 ° peel strength between the metal plate and the coating film is 1N because it can withstand squeezing and ironing. It is preferably / 15 mm or more.

<Squeezed iron can>
The squeezing can of the present embodiment can be obtained by a conventionally known squeezing method using the above-mentioned coating composition and / or coated metal plate. Since the coated metal plate of the present embodiment is excellent in moldability and lubricity, it is squeezed not only when a liquid coolant is used but also when molding is performed under dry conditions without using a liquid coolant. Ironing cans can be molded.

Specifically, the squeezed iron can of the present embodiment can be molded by the following manufacturing method.
First, prior to squeezing and ironing, it is preferable to apply a wax-based lubricant, for example, paraffin-based wax, white petrolatum, palm oil, various natural waxes, polyethylene wax, etc. to the surface of the coated metal plate, whereby dry conditions are obtained. It is possible to efficiently squeeze and iron underneath.
A painted metal plate coated with a wax-based lubricant is punched out with a cupping press, and a drawing cup is formed by a drawing method. In the present embodiment, the drawing ratio RD defined by the following formula (3) is in the range of 1.1 to 2.6 in total (up to the squeezing can), particularly in the range of 1.4 to 2.6. Is desirable. If the aperture ratio is larger than the above range, the aperture wrinkles become large, cracks may occur in the coating film, and metal exposure may occur.
RD = D / d ... (3)
In the formula, D represents the blank diameter and d represents the can body diameter.

The drawing cup is then re-squeezed-one or several steps of ironing.

In the present embodiment, it is desirable that the ironing ratio R represented by the following formula (4) is in the range of 25 to 80%, particularly 40 to 80%, more preferably 50 to 70%. If the squeezing rate is lower than the above range, the side wall of the can body cannot be sufficiently thinned, which is not sufficiently satisfactory in terms of economy. On the other hand, if the squeezing rate is higher than the above range, the metal is exposed. There is a risk.
R (%) = (tb-tw) / tb × 100 ... (4)
In the formula, tb represents the thickness of the original coated metal plate, and tw represents the thickness of the central portion of the side wall of the can body of the squeezed iron can.

Further, in the squeezed iron can of the present embodiment, the thickness of the central portion (the thinnest portion) of the side wall of the can body is 20 to 75%, preferably 20 to 60% of the thickness of the bottom (central portion) of the can. The thickness, more preferably 30 to 50%, is preferable. Further, when a squeezed iron can is formed from a painted metal plate by squeezing and ironing, the thickness of the coating film located on the body of the can becomes as thin as the metal base material by the processing. Therefore, the thickness of the coating film at the center of the side wall of the can body is 20 to 75%, preferably 20 to 60%, more preferably 30 to 50% of the thickness of the coating film at the center of the bottom of the can, which is hardly thinned during can manufacturing. It is preferable that the thickness is as high as.

The obtained squeezed iron can is subjected to doming molding at the bottom and trimming of the open edge according to a conventional method. Then, if desired, it is subjected to one-stage or multi-stage neck-in processing, and flange processing is performed to obtain a can for winding. Further, after forming a squeezed iron can, the upper portion thereof can be deformed to form a bottle shape, or the bottom portion can be cut off and another can end can be attached to form a bottle shape.

The squeezed iron can of the present embodiment is a squeezed iron can having a coating film on the inner surface and / or the outer surface, and can be formed by using the above-mentioned coating composition, but the coating film is the main ingredient. The resin contains a polyester resin having a glass transition temperature of 60 ° C. or higher, a resole-type phenol resin and / or an amino resin as a curing agent, and an organic sulfonic acid-based acid catalyst and / or a phosphoric acid-based acid catalyst as a curing catalyst. The content of the curing catalyst with respect to 100 parts by mass of the main resin is less than 0.3 parts by mass, and the thickness of the coating film at the center of the side wall of the can body is 20 to 75% of the thickness of the coating film at the bottom of the can. It is characterized by being.

In the squeezed iron can of the present embodiment, the content of the curing catalyst with respect to 100 parts by mass of the base resin is preferably less than 0.3 parts by mass, more preferably 0.1 parts by mass or less, and particularly preferably 0.03 to 0. It is characterized by having 1 part by mass.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples. In the examples and comparative examples, the part simply referred to as a part indicates a mass part.

(Example 1)
[Adjustment of inner surface coating composition]
As the main resin, polyester resin (a) (non-crystalline polyester resin, acid value: 2 mgKOH / g, Tg: 80 ° C., Mn = 18,000, monomer composition: terephthalic acid component / isophthalic acid component / ethylene glycol component / propylene glycol Ingredients = 38/12/17/33 mol%), as a curing agent, an m-cresol-based resol-type phenol resin in which a methylol group was alkoxymethylated with n-butanol (ratio of etherified methylol groups: 90 mol%, Mn = 1,200), and dodecylbenzenesulfonic acid (amine neutralized product) was used as the curing catalyst (acid catalyst).

The polyester resin (a) was dissolved in a mixed solvent of methyl ethyl ketone / solvent naphtha = 50/50 (mass ratio) to obtain a polyester resin (a) solution having a solid content of 30% by mass. An n-butanol solution (solid content 50% by mass) of the resol-type phenol resin was diluted with methyl ethyl ketone to obtain a resol-type phenol resin solution having a solid content of 30% by mass. Dodecylbenzenesulfonic acid was amine-neutralized with 2-dimethylaminoethanol and then dissolved in isopropanol to obtain an acid catalyst solution having a solid content of dodecylbenzenesulfonic acid of 30% by mass.

Next, using 333 parts of the polyester resin (a) solution (100 parts of solid content), 33 parts of the resole-type phenol resin solution (10 parts of solid content), and 0.33 parts of the acid catalyst solution (0.10 part of solid content). Adjust the coating composition [solid content concentration: about 30% by mass, solid content mixing ratio: polyester resin (a) / curing agent / acid catalyst (dodecylbenzene sulfonic acid) = 100/10 / 0.1 (mass ratio)] bottom.

[Adjustment of exterior paint composition]
A polyester resin (a) was used as the polyester resin, an amino resin (methyl etherified melamine resin) was used as the curing agent, and dodecylbenzenesulfonic acid (amine neutralized product) was used as the curing catalyst (acid catalyst).

Similar to the preparation of the coating composition for the inner surface, a polyester resin (a) solution having a solid content of 30% by mass and an acid catalyst solution of dodecylbenzenesulfonic acid were obtained. The amino resin was diluted with methyl ethyl ketone to obtain an amino resin solution having a solid content of 30% by mass. Next, a coating composition using 333 parts of the polyester resin a solution (100 parts of solid content), 20 parts of the amino resin solution (6 parts of solid content), and 0.33 parts of the acid catalyst solution (0.10 part of solid content) [ The solid content concentration: about 30% by mass, the solid content mixing ratio: polyester resin (a) / curing agent / acid catalyst (dodecylbenzenesulfonic acid) = 100/6 / 0.1 (mass ratio)] was adjusted.

The following measurement items of the polyester resin followed the following method.
(1) Measurement of Number Average Molecular Weight of Polyester Resin It was measured by gel permeation chromatography (GPC) using a standard polystyrene calibration curve.

(2) Measurement of glass transition temperature Measurement was performed at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC).

(3) Measurement of acid value According to the test method of the neutralization titration method of JIS 0070, 4 g of polyester resin was dissolved in 20 ml of chloroform and titrated with 0.1 N KOH ethanol solution to obtain the resin acid value (mgKOH / g). Asked. Phenolphthalein was used as an indicator.

(4) Measurement of Monomer Composition 30 mg of a solid polyester resin was dissolved in 0.6 mL of deuterated chloroform, ^{measured by 1} H-NMR, and the monomer composition ratio was determined from the peak intensity. The composition ratio was determined by removing a very small amount of components (less than 1 mol% with respect to all monomer components).

A coated metal plate and a squeezing can using the same were prepared from the above-mentioned inner surface coating composition and outer surface coating composition, and each evaluation described later was performed.

[Creation of painted metal plate]
A phosphoric acid chromate-based surface-treated aluminum plate (3104 alloy, plate thickness: 0.27 mm, chromium weight in the surface-treated film: 20 mg / m ² ) was used as the metal plate, and first, the surface to be the outer surface side after molding was dried. The exterior coating composition was coated with a bar coater and dried at 120 ° C. for 60 seconds so that the coating weight after baking was 40 mg / dm ^2. Then, on the surface on the opposite inner surface side, the coating composition for the inner surface was coated with a bar coater so that the coating film weight after drying and baking was 90 mg / dm ^2, and the temperature was 250 ° C. (the temperature inside the oven). It was prepared by baking for 30 seconds.

The evaluation of the painted metal plate was carried out according to the following method.
(5) Substrate adhesion evaluation (180 ° peel test)
From the coated metal plate produced as described above, as shown in FIG. 1A, a strip-shaped test piece having a height of 50 mm and a width of 30 mm so that the rolling (roll) direction of the metal base material is the long side. 1 was cut out. Using a utility knife, two scratches 2 substantially parallel to the longitudinal direction were made at positions 7.5 mm from both ends of the evaluation surface so as to reach the base material of the metal base material m vertically from the strip-shaped tip. The width between the two scratches 2 corresponds to 15 mm. Next, a scratch 3 was made on the back side of the evaluation surface at a position 15 mm from the tip of the long side of the strip shape so as to be parallel to the width direction (FIG. 1 (b)). Next, using metal scissors or the like, a cut 6 was made from the lower part 5 of the test piece toward the upper part 4 of the test piece along the wound 2 until the wound 3 was reached (FIG. 2). The end 1a of the test piece between the cuts 6 is bent so that the coating film 8 on the evaluation surface is on the inside starting from the scratch 3, leaving the ends 1b on both sides of the cut 6, and 2 along the scratch 3. The base material m was cut in the width direction only between the scratches 2 at the site. At this time, in the peel strength evaluation unit 7, the coating film 8 on the evaluation surface is not cut and remains connected to each of the cut and separated metal plates (FIG. 3 (b)). On the other hand, the coating film 9 on the back surface is cut along the scratch 3. A 180 ° peel (peeling) test was performed at a tensile speed of 5 mm / min at 23 ° C. using a tensile tester (“Autograph AG-IS” manufactured by Shimadzu Corporation) to measure the peel strength (peeling strength).

When the coating film of the measuring part was uniformly peeled by the 180 ° peel test, the peeling strength was read as the average value of the region where the strength was stable at 5 to 10 mm (1 to 2 minutes from the start of measurement) from the measurement start part.

The evaluation unit 7 forcibly peeling the coating film 8 from the base material m was visually observed, and the coating film 8 of the evaluation unit 7 was completely peeled off from the base material, and the coating film 8 remained on the base material m after the peeling. If not, it is evaluated that the coating film has peeled off the interface, and the coating film 8 has high adhesion to the base material m. It was evaluated as having coagulated fracture.
Evaluation results are: ◎: Peeling strength is 2.0N / 15mm or more due to interfacial peeling or cohesive failure ○: Peeling strength is less than 2.0N / 15mm due to interfacial peeling 1.0N / 15mm or more,
Δ: Peeling strength is less than 1.0 N / 15 mm due to interfacial peeling, 0.5 N / 15 mm or more,
X: The peel strength was less than 0.5 N / 15 mm in the interfacial peeling.

(6) Curability evaluation (MEK extraction evaluation)
A coated metal plate in which only the coating film on the inner surface side is formed is produced by the same method as above, a test piece having a size of 5.0 cm × 5.0 cm is cut out from the obtained coated metal plate, and after measuring the mass of the test piece (W1). ), 200 ml of MEK (methyl ethyl ketone) was used, and the test piece was immersed in boiling MEK (under reflux at 80 ° C.) for 1 hour, and MEK extraction was performed at the boiling point for 1 hour. The test piece after extraction was washed with MEK, dried at 120 ° C. for 1 minute, and the mass (W2) of the test piece after extraction was measured. Further, the coating film was removed by a decomposition method using concentrated sulfuric acid, and the mass (W3) of the test piece was measured. The MEK extraction rate of the coated plate, which indicates the degree of curing of the coating film of the coated metal plate, is calculated by the following formula (5).
MEK extraction rate% = 100 × (W1-W2) / (W1-W3) ... (5)
The evaluation results were: ⊚: less than 10% ◯: 10% or more and less than 20% Δ: 20% or more and less than 30% ×: 30% or more.

(7) Preparation of Squeezing Iron Can A shallow squeezing cup was prepared by applying paraffin wax to both sides of the coated metal plate prepared by the above method and then punching it into a circle having a diameter of 142 mm. Next, the shallow drawing cup is re-drawn, ironed (3 steps), and domed under dry conditions, and the drawing can (can diameter: 66 mm, height: about 130 mm, total drawing ratio: 2. 15. Ironing rate: 64%, thickness at the center of the side wall of the can body: 38.5% of the thickness at the center of the bottom of the can).

(8) Evaluation of can manufacturing processability (can body ERV test)
A metal exposed part is formed on the outer surface side of the bottom of the squeezed iron can prepared by the above method, and the can body is connected to the anode of the enamelator. Was immersed in a saline solution filled in a can, and a voltage of 6.30 V was applied for 4 seconds at room temperature, and then the current value was measured. In such a measurement, it is shown that the more the current flows, the more defects exist in the coating film layer which is an insulator, and the metal on the inner surface of the can is exposed.
The evaluation result is
⊚: Current value less than 50 mA ◯: Current value 50 mA or more and less than 100 mA Δ: Current value 100 mA or more and less than 300 mA ×: Current value 300 mA or more.

(9) Evaluation of processing adhesion By observing the open end of the squeezed iron can created by the above method and visually observing the degree of peeling of the coating film in the vicinity of the opening end, adhesion during can manufacturing (processing adhesion). Was evaluated.
Evaluation result is ◯: No peeling of the coating film is confirmed near the opening edge.
X: Peeling of the coating film is confirmed in the vicinity of the open end.
Shown in.

(10) Flavor sorption evaluation (flavor sorption test)
A test piece having a size of 2.5 cm x 5.0 cm is cut out from the bottom of the squeezed iron can produced by the above method at a height of 8.0 cm, and the coating film on the outer surface side is sandpaper (sandpaper). ), Washed and dried. A 5% ethanol aqueous solution containing 2 ppm of limonene was prepared as a model flavor test solution. The model flavor test solution was placed in a glass bottle with packing (Duran bottle), the test piece was immersed and sealed, and stored at 30 ° C. for 2 weeks. The test piece was taken out from a glass bottle, washed with water, water droplets were removed, immersed in 50 mL of diethyl ether, sealed, and stored at room temperature for a whole day and night. The extract was concentrated with a concentrator and subjected to GC-MS analysis (gas chromatography-mass spectrometry). From the limonene-derived component peak obtained by GC-MS analysis, the amount of limonene was determined by a calibration curve, and the ratio to the amount of limonene charged was determined as the limonene accretion rate (%) from the following formula (6).
Limonene collection rate (%) = Limonene collection amount / Limonene charge amount x 100 ... (6)
The evaluation result is
◯: Limonene sorption rate is less than 2% ×: Limonene sorption rate is 2% or more.

(Examples 2 to 9, Comparative Examples 1 to 4)
As shown in Table 1, the coating composition for the inner surface was prepared by changing the type of polyester resin and the solid content blending ratio, and the same procedure as in Example 1 was carried out for evaluation. The results are shown in Table 1. As the polyester resin, in addition to the above-mentioned polyester resin, the polyester resin (b) (non-crystalline polyester resin, acid value: 22 mgKOH / g, Tg: 82 ° C., Mn = 6,000, monomer composition: terephthalic acid component / Trimellitic acid component / ethylene glycol component / propylene glycol component = 49/1/12/38 mol%), polyester resin (c) (non-crystalline polyester resin, acid value: 2 mgKOH / g, Tg: 84 ° C., Mn = 18,000, monomer composition: terephthalic acid component / ethylene glycol component / propylene glycol component = 50/14/36 mol%), polyester resin (d) (acid value: 11 mgKOH / g, Tg: -25 ° C, Mn = 17, 000, monomer composition: terephthalic acid component / isophthalic acid component / sebacic acid component / 1,4-butanediol component = 14/17/19/50 mol%), polyester resin (e) (non-crystalline polyester resin, acid value: 3 mgKOH / g, Tg: 40 ° C., Mn = 15,000, monomer composition: terephthalic acid component / isophthalic acid component / sebacic acid component / ethylene glycol component / propylene glycol component / neopentyl glycol component / 1,4-butanediol component = 25/20/5/16/14/3/17 mol%) was used.

It is clear that the coated metal plate using the coating composition of the present invention and the squeezing can using the same have all of can-making processability, substrate adhesion, and flavor-adhesion resistance.

The present invention can be suitably used in the field of metal processing that considers the environment while maintaining a high degree of can manufacturing processability.

1 Test piece 1a End 1b End 2 Scratch a
3 wound b
4 Upper part of test piece 5 Lower part of test piece 6 Cut 7 Evaluation part 8 Coating film (evaluation surface)
9 coating film

Claims (12)

It contains a polyester resin having a glass transition temperature of 60 ° C. or higher as a main resin, a resole-type phenol resin and / or an amino resin as a curing agent, and an organic sulfonic acid-based acid catalyst and / or a phosphoric acid-based acid catalyst as a curing catalyst. A coating composition, wherein the content of the curing catalyst with respect to 100 parts by mass of the main resin is less than 0.3 parts by mass. The coating composition according to claim 1, wherein the content of the curing catalyst with respect to 100 parts by mass of the main resin is 0.1 parts by mass or less. The coating composition according to claim 1 or 2, wherein the acid value of the main resin is less than 20 mgKOH / g. The coating composition according to any one of claims 1 to 3, wherein the content of the curing agent is 4 to 30 parts by mass with respect to 100 parts by mass of the main resin. A coated metal plate for a squeezing can, wherein a coating film of the coating composition according to any one of claims 1 to 4 is formed on a metal surface of at least one side of the metal plate. The coated metal plate for a squeezing can according to claim 5, wherein the 180 ° peel strength of the coating film is 1 N / 15 mm or more. A squeezed iron can made of a coated metal plate for a squeezed iron can according to claim 5 or 6. The squeezing can according to claim 7, wherein the thickness of the coating film at the center of the side wall of the can body on the inner surface and / or the outer surface is 20 to 75% of the thickness of the coating film on the bottom of the can. A method for producing a squeezed iron can, which comprises squeezing and ironing a coated metal plate for a squeezed iron can according to claim 5 or 6 at a squeezing rate of 25 to 80%. A squeezed iron can having a coating film on the inner surface and / or outer surface, wherein the coating film is a polyester resin having a glass transition temperature of 60 ° C. or higher as a main resin, and a resole-type phenol resin and / or an amino resin as a curing agent. It contains an organic sulfonic acid-based acid catalyst and / or a phosphoric acid-based acid catalyst as a curing catalyst, the content of the curing catalyst with respect to 100 parts by mass of the main resin is less than 0.3 parts by mass, and the central portion of the side wall of the can body. A squeezing can in which the thickness of the coating film is 20 to 75% of the thickness of the coating film on the bottom of the can. The squeezing can according to claim 10, wherein the content of the curing catalyst with respect to 100 parts by mass of the main resin is 0.1 parts by mass or less. The squeezing can according to claim 10 or 11, which is formed from a coated metal plate having a coating film on at least one side of the metal plate.

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